Electronic control unit and electric power steering system

ABSTRACT

An electronic control unit is provided for an electric power steering system. The electric power steering system includes a housing and an electric motor. The electronic control unit is arranged inside the housing and is electrically connected to the electric motor. The electronic control unit includes a first power board having a first electric motor connector for electric connection with the electric motor, and a second power board having a second electric motor connector for electric connection with the electric motor. A connector plate of the electronic control unit is electrically connected by at least one plug connector to the first power board via at least one first power connector, and to the second power board via at least one second power connector. The at least one first power connector is shorter than the at least one second power connector. An electric power steering system is also provided.

CROSS REFERENCE

This application claims priority to and is a continuation of PCTApplication No. PCT/EP2020/062850, filed May 8, 2020, the entirety ofwhich is hereby incorporated by reference.

FIELD OF THE INVENTION

The invention is directed at an electronic control unit for an electricpower steering system and an electric power steering system.

BACKGROUND OF THE INVENTION

In the electric power steering system, the electronic control unit canbe connected with an electric motor for supplying power to the electricmotor from a power source such as a battery. The electric power steeringsystem can assist in a handling operation, typically a steering, of atransportation equipment by a driver. The transportation equipment canbe an automobile.

The electric power steering system may further comprise a torque sensor,a steering shaft, a handle, typically a steering wheel, and the powersource. In the following, a typical arrangement and operation of theelectric power steering apparatus in an automobile will be described.

The torque sensor may be mounted on the steering shaft. Upon rotatingthe steering shaft by operating the handle, the torque sensor detects atorque being applied to the steering shaft by the operation of thehandle. Upon detection of the torque by means of the torque sensor, atorque signal is output from the torque sensor to the electronic controlunit. The electronic control unit then drives the electric motor basedat least on the torque signal. Optionally, the control device mayinclude further data such as vehicle speed in addition to the torquesignal for controlling the driving of the electric motor.

The electronic control unit drives the electric motor by supplying adriving current from the power source, such as the battery of theautomobile, to the electric motor. A driving force generated from theelectric motor is then transmitted to the wheels directly or via agearbox depending on the configuration in the automobile. As a result,the electric power steering apparatus changes a steering angle of thewheels by amplifying the torque of the steering shaft by means of theelectric motor. This enables the driver to operate the handle with lessforce.

The electronic control unit comprises a power board electricallyconnected with the electric motor. The power to the electric motor istransmitted via this power board. Thereby, the power board generatesheat during operation of the electronic control unit. To preventoverheating and damage of the electronic control unit, a heat sink maybe provided inside of the electronic control unit and arranged inthermal contact with a housing of the electric power steering system orelectric motor.

DE 10 2016 212 862 A1 describes a power unit for an electric steeringsystem. The power unit comprises a motor housing for a motor, a heatsink and control electronics for the motor attached to the heat sink.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to improve the electroniccontrol unit for an electric power steering system and an electric powersteering system known from the state of the art, in particular toprovide an electronic control unit for an electric power steering systemand an electric power steering system having improved assemblycharacteristics, in particular a compact, low-cost and easy-to-assembledesign.

This problem is solved by an electronic control unit as disclosedherein. The features and details described in connection with theelectronic control unit of the invention apply in connection with theelectric power steering system and the other way around, so thatregarding the disclosure of the individual aspects of the invention itis or can be referred to one another.

According to a first aspect of the invention, the problem is solved byan electronic control unit for an electric power steering system, theelectric power steering system comprising a housing and an electricmotor, the electronic control unit being configured to be arrangedinside the housing and to be electrically connected to the electricmotor, whereby the electronic control unit comprises a first power boardhaving a first electric motor connector for electric connection with theelectric motor, a second power board having a second electric motorconnector for electric connection with the electric motor, and whereby aconnector plate of the electronic control unit is electrically connectedby means of at least one plug connector of the connector plate to thefirst power board via at least one first power connector and to thesecond power board via at least one second power connector, wherein theat least one first power connector is shorter than the at least onesecond power connector.

By means of providing different lengths of the first power connector andthe second power connector, improved assembly characteristics, inparticular a compact, low-cost and easy-to-assemble design, of theelectronic control unit are achieved. That is, the first power board andthe second power board may be arranged at different distances from theconnector plate. Further, the first power board and the second powerboard may be arranged parallel to one another.

In particular, the first power connector may have a first lengthcorresponding to a distance of the first power board from the connectorplate and the second power connector may have a second lengthcorresponding to a distance of the second power board from the connectorplate, whereby the first length is smaller than the second length.

The first power board and the second power board may in particular beprovided as printed circuit boards. The two power boards may compriseelectronic components such as coils and capacitors for enabling thepower board to transmit power from a power source to the electric motor.

The electric motor may in particular be arranged inside the housing. Thehousing may in particular be an electric motor housing, i.e. the housingof the electric motor. The housing may in particular have a tubularshape. The housing may further in particular have a circular orelliptical cross section. Also, the housing may be made from aheat-conducting material. The heat-conducting material may in particularbe or comprise a metal such as aluminum, magnesium, copper or similar.

In particular, the two power boards may be separately from one anotherconnected to the connector plate and thereby to the power source. Theconnector plate may be made from plastic, for example. The connectorplate may be formed as a cap for sealing the housing at an end thereof.The connector plate may be provided with a sealing for sealing theinside of the housing against the outside. The sealing may be made froma silicone rubber. The connector plate may comprise one, two, three ormore connectors, in particular plug connectors. At or inside of the plugconnectors, the connector plate may be provided with electricalcontacts. The electrical contacts may be made from a copper alloy, forexample, to provide great electrical conductivity. One or multiple ofthe plug connectors may be provided for contacting the control board ofthe transportation equipment with the logic board. Thereby, the torquesensor, other sensors and/or other electronic control units may beconnected to the logic board. The plug connectors may be connected bymeans of power connectors to the power boards.

It is possible, that the connector plate is connected to the first powerboard via two first power connectors and to the second power board viatwo second power connectors, wherein both first power connectors areshorter than both second power connectors.

Further, it is possible, that the at least one first power connectorand/or the at least one second power connector are provided as metalstrips. In particular, the metal strips may be provided as metal sheets.Aluminum, copper, alloys of the aforementioned or other metal havinghigh electrical conductivity may be used for the metal strips. The atleast one first power connector and the at least one second powerconnector may have flat and/or rectangular shape. The metal strips maybe bent along their length such that they are positioned in theelectronic control unit according to the defined geometry of other partsof the electronic control unit such as the power boards and the logicboard.

It is further possible, that the at least one second power connector hasat least 120%, in particular at least 150% and further in particular atleast 200%, of the length of the first power connector. Thereby, a largeheat sink, i.e. having a large thickness, may be arranged in between thetwo power boards for providing good heat dissipation characteristics.

It is possible, that each of the first power board and the second powerboard is provided with three phases of electricity to supply three-phaseelectric power to the electric motor. Thereby, both power boards areable to provide the electric motor with three-phase electric powerindependent from one another. Further, it is possible, that the firstpower board and the second power board are arranged to supplythree-phase electric power to the electric motor upon failure of theother one of the first power board and the second power board. For thispurpose, a logic board of the electronic control may be arranged todetect failure of one of the two power boards and instruct thefunctioning power board to drive the electric motor. Further, it ispossible, that the first power board and the second power board arearranged as redundant power boards to supply six phases of electricityto the electric motor. For this purpose, the electric motor may be asix-phase electric motor. Thereby, a better and more reliable powertransmission to the electric motor may be achieved. In particular, ifone power board of the two power boards fails, the other one may stillbe operated to provide the electric motor with electricity. Thus, theelectric motor can be separately driven by the driving current suppliedseparately by any one or both of the two power boards. Thereby, it canbe ensured that the electronic control unit can safely provide theelectric motor with electricity even when one of the two power boardsfail. This provides for a redundant and failure unsusceptible design ofthe electronic control unit and the electric power steering system.

Further, it is possible, that the logic board is sandwiched in betweenthe first power board and the connector plate. The logic board may inparticular be provided as a printed circuit board. The logic board doesnot have to be attached to a heat sink of the electronic control unit.In particular, the logic board may not be attached to the heat sink. Thelogic board in operation of the electronic control unit generates lessheat than the two power boards and thus it may be prioritized that thetwo power boards that are generating more heat in operation of theelectronic control unit are attached to the heat sink.

Thereby, it is possible that the logic board is logically connected toat least one of the at least one plug connector of the connector plateby means of at least one signal connector. Thereby, the connector plateis logically connected to the logic board separate from its powerconnection with the power boards.

It is also possible, that the first power board comprises at least onefirst power board recess through which the at least one second powerconnector extends to the second power board. Thereby, the first powerconnector may be easily guided through the first power board and to thesecond power board.

It is also possible, that the electronic control unit comprises a heatsink, the heat sink being sandwiched in between the first power boardand the second power board. The first power board may be provided on oneside of the heat sink and the second power board may be provided onanother side of the heat sink. The first power board and the secondpower board may be directly attached with their circuit board andelectronic components to the heat sink. A thermal interface material maybe provided between the first power board and the heat sink and thesecond power board and the heat sink to thermally attached therespective parts with each other for better thermal conductivity.

Both power boards may be attached to the heat sink. In particular, bothpower boards may be fitted onto the heat sink. Both power boards may besurround by a heat sink edge of the heat sink. The heat sink edge of theheat sink may comprise a groove arranged for crimping the housing intothe groove and thereby at least securing, and possibly thermallyconnecting, the heat sink with the housing. When crimping the housinginto the groove of the heat sink, a particularly tight fitting of theheat sink inside of the housing is achieved and the thermal conductivityfrom the heat sink to the housing is improved. Further, the overallcontact surface of the heat sink with the housing and thereby theoverall thermal conductivity from the heat sink to the housing is evenfurther improved. Also, providing the heat sink with the groove may beperformed at relatively low cost when manufacturing the heat sink andthe crimping of the housing into the groove is a relatively simple, fastand cost-effective way of securing the heat sink and in particular inthe entire electronic control unit with the housing of the electricpower steering system. The crimping may be performed by squeezing thehousing at its outer side into the groove. Thereby, the housing isdeformed plastically and contacted with the heat sink at its groove. Thegroove may have a rectangular, U-type or V-type shape, for example.Also, it is possible to provide more than just one groove for crimpingit with the housing in the heat sink. For example, the heat sink edge ofthe heat sink may comprise at least two grooves for crimping the housinginto the at least two grooves.

The heat sink may be configured as an at least partially circular heatplate. In particular, the heat sink may be at least a half or fullycircular heat plate. The heat sink edge of the heat sink may have orcircumscribe the circular form of the heat plate. The heat sink may be aflat plate in the sense that its thickness is less than its diameter orradius. The heat sink may comprise several heat conduction surfacesarranged in contact with electronic components of the power boards.Thermal interface material may be provided in between the electroniccomponents and the heat conduction surfaces. Thereby, heat generated bythe electronic components may be conducted to the heat sink veryeffectively. The several heat conduction surfaces may be arranged atdifferent heights along a thickness of the heat sink to accommodateelectronic components of different height. Thereby, the design freedomof the at least one power board with regard to its specific electroniccomponents, such as their size and geometry, may be maintained whilestill enabling a high thermal conductivity of the power boards to theheat sink. In other words, the heat sink may be adapted in its form andgeometry to the at least one power board and not the other way around.

It is also possible, that the heat sink comprises heat sink throughholes and the first power board is secured to the heat sink by means ofbolts passing through the heat sink through holes and being fastened indomes extending from the connector plate. This enables a simple yetreliable and detachable connection of the power boards with the heatsink and further with the connector plate.

Alternatively, or additionally, it is possible, that the heat sinkcomprises heat sink holes and the second power board is secured to theheat sink by means of bolts being fastened in the heat sink holes.Thereby, a simple yet reliable and detachable connection between thesecond power board with the heat sink is provided.

In particular, the first power board may be attached by means of theheat sink through holes and domes in the connector plate and the secondpower board may be attached by means of the holes in the heat sink. Thisprovides for particularly good serviceability, because the second powerboard may be exchanged without demounting the first power board from theheat sink and further improves the reliability of the secure connection.

It is further possible, that the heat sink comprises heat sink recessesfor the at least one second power connector, the at least one secondpower connector extending from the connector plate through the heat sinkrecesses inside of the heat sink to the second power board. The at leastone second power connector may be used for transferring current from theconnector plate, which may be connected to the power source, to thesecond power board. The heat sink recesses allow for simple yetcost-effective design of the heat sink and the at least one second powerconnector. The heat sink recesses may be designed as flat slots.

It is also possible, that the heat sink comprises a heat sink cutout, inparticular extending from a heat sink edge to an inside of the heatsink, a second logic connector extending from a logic board of theelectronic control unit through the heat sink cutout to the second powerboard. The heat sink cutout may have a partially circular and/orpartially flat shape. The heat sink cutout allows for simple yetcost-effective design of the heat sink and the second logic connector.

Thereby, it is possible, that the first electric motor connector fromthe second power board extends through the heat sink cutout forconnection with the electric motor of the electric power steeringsystem. Thereby, the number of cutouts or recesses may be reduced andthe electronic control unit may have a compact design. By means of thefirst electric motor connector, driving current from the first powerboard may be transmitted along the electronic control unit, passing bythe heat sink, to the electric motor.

Further it is possible, that the heat sink comprises heat sinkprojections projecting from the heat sink beyond the first power boardand the second power board and being arranged to rest on an inner riminside of the housing of the electric power steering system. By means ofthe heat sink projections, when installing the electronic control unitin the housing, the end position of the electronic control unit in thehousing may be easily detected. The end position is achieved when theprojections rest on the inner rim inside the housing and the electroniccontrol unit cannot be pushed into the housing any further without usingexcessive force to bend or damage the projections. Thereby, a definedposition at which the housing is crimped into the groove is provided andthe crimping can be performed at that defined position every time whenjoining the heat sink with the housing facilitating the manufacture.

According to a second aspect of the invention, the problem raised in theintroduction of this description is solved by an electric power steeringsystem comprising the electronic control unit according to the firstaspect of the invention, whereby the electric motor of the electricpower steering system is electrically connected to the first power boardby means of the first electric motor connector and to the second powerboard by means of the second electric motor connector.

When the heat sink comprises projections projecting from the heat sinkbeyond the at least one power board, the projections may rest on aninner rim inside of the housing of the electric power steering system.Thereby, a defined position of the electronic control unit in thehousing and a stable connection therewith is achieved.

The electric power steering system may further comprise a torque sensor,a steering shaft, a handle, in particular a steering wheel, and a powersource. The electric power steering system may further have thearrangement and be arranged for operation of in an automobile asdescribed in the introductory part of this description.

Further advantages, features and details of the invention unfold fromthe following description, in which by reference to drawings of thefollowing Figures an embodiment of the present invention is described indetail. Thereby, the features from the claims as well as the featuresmentioned in the description can be essential for the invention as takenalone or in an arbitrary combination.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made more particularly to the drawings, whichillustrate the best presently known mode of carrying out the inventionand wherein similar reference characters indicate the same partsthroughout the views.

FIG. 1 is an exploded illustration from a bottom side perspective viewof an embodiment of the electronic control unit according to the firstaspect of the invention.

FIG. 2 is an exploded illustration from a top side perspective view ofthe electronic control unit of FIG. 1 .

FIG. 3 is a detailed illustration from a side perspective view of twopower boards and a logic board of the electronic control unit of FIGS. 1and 2 .

FIG. 4 is a detailed illustration from a side perspective view on theassembled logic board with the connector plate.

FIG. 5 is a detailed illustration from a side perspective view on theassembled logic board with the connector plate and the assembled firstpower board.

FIG. 6 is a detailed illustration from a side perspective view on a heatsink of the electronic control unit of FIGS. 1 and 2 .

FIG. 7 is a detailed illustration from a side perspective view on theassembly of the heat sink of FIG. 6 with the assembly of the assembledlogic board with the connector plate and the first power board of FIG. 5.

FIG. 8 is a detailed illustration from a side perspective view on theassembly of the assembled logic board with the connector plate, theassembled first power board and the heat sink of FIG. 6 .

FIG. 9 is an illustration from a side perspective view on the electroniccontrol unit 100 of FIGS. 1 and 2 in an assembled state.

FIG. 10 is an illustration from a side perspective view on a process ofassembling the electronic control unit of FIG. 9 with an embodiment ofthe electric power steering system of the invention.

FIG. 11 is an illustration of a sectional cut through the electric powersteering system of FIG. 10 with the electronic control unit assembledinside.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exploded illustration of an electronic control unit 100according to an embodiment of the invention from a bottom sideperspective view. According to this bottom side perspective view, bottomsides of the parts of the electronic control unit 100 are visiblyillustrated.

FIG. 2 shows the same electronic control unit 100 of FIG. 1 with thedifference that it is from a top side perspective view. According tothis top side perspective view, top sides of the parts of the electroniccontrol unit 100 are visibly illustrated.

As can be taken from FIGS. 1 and 2 , the electronic control unit 100comprises two power boards 30, 40, namely a first power board 30 and asecond power board 40. The power boards 30, 40 may also be referred toas power-stages. The two power boards 30, 40 are arranged so as tosupply an electric motor (not shown) of an electric power steeringsystem 200 (see FIGS. 10 and 11 ) with driving current. For thispurpose, the first power board 30 is connected to a first electric motorconnector 80 electrically connectable with the electric motor. Further,for this purpose, the second power board 40 is connected to a secondelectric motor connector 90 electrically connectable with the electricmotor.

Further, the electronic control unit 100 comprises a connector plate 10.The connector plate 10 comprises multiple, in this particular embodimentthree, plug connectors 11.1, 11.2, 11.3. In this particular embodiment,the first plug connector 11.1 and the second plug connector 11.2 areprovided with electric contacts (not shown) inside thereof. The electriccontacts may be made from a copper alloy, for example, to allow for goodelectric conductivity. These electric contacts are arranged as first andsecond signal connectors 15.1, 15.2. The signal connectors 15.1, 15.2extend from the plug connectors 11.1, 11.2 on a top side of theconnector plate 10 to a bottom side of the connector plate 10.

The electronic control unit 100 also comprises a logic board 20. Thelogic board 20 is arranged so as to control the two power boards 30, 40or, in other words, the operation of the electronic control unit 100 or,in further other words, the transmission of driving current to theelectric motor. For this purpose, the signal connectors 15.1, 15.2 areconnected with the logic board 20. Further, the logic board 20 isconnected via a first logic connector 70 to the first power board 30.Also, the logic board 20 is connected via a second logic connector 60 tothe second power board 40.

Signal plugs (not shown) may be attached to the plug connectors 11.1,11.2 for supplying signals from a sensor, such as a torque sensor, orother units, such as a further electronic control unit from atransportation equipment (not shown), such as an automobile, to thelogic board 20. By means of the signals, such as a torque detected bythe torque sensor or a travelling speed of the transportation equipment,the logic board 20 may control the driving current via the two powerboards 30, 40.

The connector plate 10 further comprises a third plug connector 11.3.This third plug connector 11.3 comprises inside further electriccontacts. These electric contacts are provided as first power connectors16.1, 16.2 and second power connectors 17.1, 17.2. The second powerconnectors 17.1, 17.2 are longer than the first power connectors 16.1,16.2 such that they may accordingly connect with their respective powerboards 30, 40 at their respective distance from the connector plate 10.In this embodiment, the first power connectors 16.1, 16.2 and the secondpower connectors 17.1, 17.2 are provided as metal strips.

A power plug (not shown) may be connected to the third plug connector11.3 to provide power to the first power connectors 16.1, 16.2 andsecond power connectors 17.1, 17.2. The power plug may be attached to apower source such as a battery (not shown) of the transportationequipment. The power source is arranged as a three-phase electric powersource. The connector plate 10 may also be referred to as a power andlogic connector plate as it provides power and logic or signalprocessing connections to the respective boards 20, 30, 40 of theelectronic control unit 100.

The first power connectors 16.1, 16.2 are connected to the second powerboard 40 and the second power connectors 17.1, 17.2 are connected to thefirst power board 30. Thereby, the first power board 30 is provided witha three-phase electric current and the second power board 40 is providedwith a three-phase electric current. The electronic control unit 100 isthereby provided with six phases and the electric motor may be providedas a six-phases electric motor. When one of the two power boards 30, 40fails due to an error, the other one can ensure safe and reliableoperation of the electric motor by transmitting driving current to it.Thereby, it is prevented that an error in one of the power boards 30, 40leads to undesirable loss of the steering function and possibly in anaccident and damage of the driver and passengers of the transportationequipment.

As can further be taken from FIGS. 1 and 2 , a heat sink 50 is arrangedin between the first power board 30 and the second power board 40. Theheat sink 50 is thus sandwiched in between the two power boards 30, 40.The heat sink 50 in this embodiment is provided as a die-cast aluminum.The heat sink 50 allows for the heat generated in the two power boards30, 40 to be dissipated away. For this purpose, the heat sink 50 isconnected to a housing 210 of the electric power steering system 200,which will be explained later in more detail.

Also, the connector plate 10 comprises a venting opening 13 and aventing element (not shown) for closing the venting opening 13. When theelectronic control unit 100 is inserted into the housing 210, which alsowill be explained in more detail letter, the venting element providesfor pressure compensation of the inside of the housing 210 with theenvironment. Further, the connector plate 10 comprises a sealing 12. Thesealing 12 is made from a silicone rubber in this particular embodiment.The sealing 12 seals the electronic control unit 100 inside the housing210 against the environment when it is inserted into the housing 210.

FIG. 3 shows the logic board 20, first power board 30 and second powerboard 40 in more detail in an exploded view. The logic board 20comprises first electronic components 21, of which the first electroniccomponents 21.1, 21.2, 21.3 are exemplary denominated. Further, thefirst power board 30 comprises second electronic components 31, of whichthe second electronic components 31.1, 31.2, 31.3 are exemplarydenominated. Moreover, the second power board 40 comprises thirdelectronic components 41, of which the third electronic components 31.1,31.2, 31.3 are exemplary denominated.

The first electronic components 21 may be coils, capacitors, at leastone computing unit, such as a processor, and other electronic componentsfor enabling calculation operations based on received signals and logiccommunication of the logic board 20 with the two power boards 30, 40.The second and third electronic components 31, 41 may be coils,capacitors and other electronic components for enabling the respectivepower board 30, 40 to transmit power from a power source to the electricmotor as will be explained further later.

The logic board 20, the first power board 30 and the second power board40 are shown in an orientation with their respective top sides andbottom sides such as they are arranged within the electronic controlunit 100. Thus, the largest of the second electronic components 31.1,31.2, 31.3 on a bottom side of the first power board 30 show towards thelargest of the third electronic components 41.1, 41.2, 41.3 of thesecond power board 40. These large electronic components 31, 41 generatea lot of heat and by virtue of this arrangement a heat sink 50 mayreceive the second and third electronic components 31, 41 to allow forgood heat conductivity characteristics so as to remove the heat from thetwo power boards 30, 40 via the heat sink 50 and housing 210effectively.

Further, the first power board 30 comprises first power board recesses32.1, 32.2 for guiding the second power connectors 16.1, 16.2therethrough. Also, the first power board 30 comprises power boardthrough holes 33.1, 33.2, 33.3 for guiding bolts 1 therethrough forfastening the heat sink 50 to the connector plate 10. These featureswill be explained later in more detail.

FIG. 4 shows an assembly of the logic board 20 with the connector plate10. The first and second signal connectors 15.1, 15.2 are connected tothe logic board 20. In particular, the first and second signalconnectors 15.1, 15.2 comprise multiple pins being attached tocorresponding pin receiving holes in the logic board 20.

The logic board 20 comprises two logic connectors 60, 70 connectedthereto and having the purpose of enabling communication and control ofthe two power boards 30, 40 by means of the logic board 20. Therefore,each of the two logic connectors 60, 70, namely the first logicconnector 70 and the second logic connector 60, comprises multipleelectrical connector pins (not denominated). The electrical connectorpins of the first logic connector 70 are relatively shorter than theelectrical connector pins of the second logic connector 60. The reasonfor this is that the first logic connector 70 connects the logic board20 with the first power board 30, whereby the distance between the logicboard 20 and the first power board 30 in an assembled state of theelectronic control unit 100 is relatively short. However, the distancebetween the logic board 20 and the second power board 40, which areconnected by means of the second logic connector 60, is relativelylonger because the first power board 30 and the heat sink 50 arearranged in between as can be seen in the assembled state of theelectronic control unit 100 from FIG. 10 , for example.

The electrical connector pins are inserted into corresponding connectorpin holes (not denominated) inside the logic board 20. The connector pinholes for the respective electrical connector pins are arranged at twoopposite ends of the logic board 20. Thereby, the first logic connector70 and the second logic connector 60 are arranged at the two oppositeends of the logic board 20. Further, the logic board 20 comprisesconnection pin holes (not denominated) for corresponding firstconnection pins (not denominated) of the first logic connector 70 andconnection pin holes for corresponding second connection pins (notdenominated) of the second logic connector 60. By means of theconnection pins the two logic connectors 60, 70 are securely fastened inthe logic board 20.

The electrical connector pins are arranged in logic connector housings71, 61 of the logic first logic connector 70 and the second logicconnector 60. In this particular embodiment, the second logic connectorhousing 61 consists of two separate parts. This design may be chosen dueto the long extension of the its electrical connector pins. The firstpart of the second logic connector housing 61 comprises the connectionpins for corresponding connection pin holes of the logic board 20 andthe second part of the second logic connector housing 61 comprisesconnection pins for securing them in corresponding connection pin holesof the second power board 40. Moreover, the first logic connectorhousing 71 comprises connection pins for securing them in correspondingconnection pin holes of the first power board 30.

As may be taken from this Figure, the logic board 20 comprises cutoutsat its edge for domes 18.1, 18.2, 18.3 projecting from the connectorplate 10 towards and beyond the logic board 20. These domes 18.2, 18.3enable fastening of the heat sink 50 with the connector plate 10 andthereby sandwiching the logic board 20 and the first power board 30 inbetween these as will be explained later. The domes 18.2, 18.3 may beprovided with molded holes inside. The molded holes may be pre-threadedfor bolts 1 or threaded by means of self-tapping bolts or screws 1.

The first power connectors 17.1, 17.2 are extending from the connectorplate 10 through a cutout (not denominated) at the edge of the logicboard 20 towards the first power board 30. Further, the second powerconnectors 16.1, 16.2 extend from the connector plate 10 next to logicboard 20 and the first power connectors 17.1, 17.2 towards the secondpower board 40.

FIG. 5 shows an assembly of the first power board 30 with the logicboard 20 and the connector plate 10.

A first electric motor connector 80 comprises three first electric phasepins 82.1, 82.2, 82.3 for electric connection with the electric motor ofthe electric power steering system 200. The three first electric phasepins 82.1, 82.2, 82.3 are received in a first electric motor connectorhousing 81. The first electric motor connector housing 81 comprisesconnection pins (not denominated) for connection with correspondingconnection pin holes (not denominated) in the first power board 30.Further, the three first electric phase pins 82.1, 82.2, 82.3 compriseat ends opposite of the ends for connecting with corresponding electricmotor pins (not shown) of the electric motor several first power boardconnection pins (not shown) for electrically connecting these with thefirst power board 30.

The first logic connector 70 is connected with the first power board 30.Further, the second power connectors 16.1, 16.2 are guided through thefirst power board recesses 32.1, 32.2 of the first power board 30.

The first electric motor connector 80 is arranged next to the secondlogic connector 60 such that they may extend together along a heat sinkcutout 53 as shown in the heat sink 50 of FIG. 6 . The first electroniccomponents 31 of the first power board 30 extend towards the heat sink50 to be arranged on the top side of the first power board 30.

FIG. 6 shows the heat sink 50 in more detail and from its bottom side. Aheat sink edge 59 of the heat sink 50 circumscribes the heat sink 50.The heat sink 50, in particular the heat sink edge 59, comprises thegroove 51 for crimping the housing 210 of the electric power steeringsystem 200 into the groove 51. Thereby, the housing 210 is mechanicallysecured to the heat sink 50 and ultimately to the electronic controlunit 100. Further, the heat sink 50 is thermally connected to thehousing 210 such that the heat generated by the two power boards 30, 40may be dissipated via the heat sink 50 along the housing 210 having amuch larger surface area for dissipation. Also, the surface area of thehousing 210 may be in thermal connection with the environment such thatthe housing 210 is cooled or, in other words, may exchange heat with theenvironment.

The groove 51 is a circumferential groove 51 such that it is arrangedaround the circumference of the heat sink edge 59. The heat sink edge 59further comprises two circumferential outer surfaces 58.1, 58.2, inbetween which the circumferential groove 51 is provided. The twocircumferential outer surfaces 58.1, 58.2 of the heat sink edge 59 areconfigured to contact an inner surface 211 of the housing 210 as may betaken from FIG. 17 . For this purpose, the outer diameter of thecircumferential outer surfaces 58.1, 58.2 equals or substantially equalsthe inner diameter of the inner surface 211 of the housing 210.

The structure of the heat sink 50 will in the following be furtherexplained with reference to FIGS. 7 and 8 , FIG. 7 showing a process ofassembling the heat sink 50 with the first power board 30 assembled withthe logic board 20 and the connector plate 10 and FIG. 8 showing theassembly according to the process of FIG. 7 . FIG. 7 and FIG. 8 show atop side of the heat sink 50 whereas FIG. 6 shows a bottom side of theheat sink 50.

The heat sink 50 is configured as a circular heat plate, whereby theheat sink 50 comprises a heat sink cutout 53. The heat sink cutout 53extends from the heat sink edge 59 to an inside of the heat sink 50. Thesecond logic connector 60 and the first electric motor connector 80extend through the heat sink cutout 53 in the assembled state where theheat sink 50 is attached to the first power board 30 as can be seen inFIG. 9 .

Further, the heat sink 50 comprises several heat conduction surfaces 52on its bottom side and on its top side for attaching them to the firstpower board 30 and the second power board 40, in particular the firstelectronic components 31 and the second electronic components 41, bymeans of a thermal interface material (not shown). The heat conductionsurfaces 52.1, 52.2 on the bottom side and the heat conduction surface52.3 on the top side are exemplary denominated in the FIGS. 6 and 8 . Inthe assembled state of FIG. 8 , the first electronic components 31 ofthe first power board 30 are in direct contact via the thermal interfacematerial with the heat conduction surfaces 52.1, 52.2 on the bottom sideof the heat sink 50. The heat conduction surfaces 52.1, 52.2 of thebottom side are arranged at different heights along a thickness of theheat sink 50 and thereby can accommodate or attach to first electroniccomponents 31 of different size or height. The same can be applied tothe top side such that heat conduction surfaces 52 of the top side ofthe heat sink 50 may be arranged at different heights along thethickness of the heat sink 50. Thereby, the first electronic components31 are effectively transferring heat to the heat sink 50.

Moreover, the heat sink 50 comprises heat sink through holes 54.1, 54.2,54.3 as can be seen in FIG. 10 from the bottom side and in FIG. 11 fromthe top side. The first power board 30 is secured by means of bolts 1passing through the heat sink through holes 54 and being fastened in thedomes 18.1, 18.2 of the connector plate 10. The bolts 1 further passthrough the power board through holes 33.1, 33.2, 33.3 of the firstpower board 30 as shown in Figure.

Also, the heat sink 50 comprises heat sink recesses 15 for guiding thesecond power connectors 16.1, 16.2 of the connector plate 10therethrough. This enables for the second power connectors 16.1, 16.2 tobe connected to the second power board 40 when the heat sink 50 isattached to the first power board 30.

Moreover, the heat sink 50 comprises heat sink projections 57.1, 57.2,57.3 projecting from the heat sink 50 beyond the two power boards 30, 40in the assembled state of the electronic control unit 100 as can be seenin FIG. 10 . These heat sink projections 57.1, 57.2, 57.2 may bearranged resting on an inner rim 212 inside of the housing 210 of theelectric power steering system 200.

The heat sink 50 also comprises heat sink holes 56.1, 56.2, 56.3 on itstop side. The second power board 40 may be fastened to the heat sink 50by means of bolts 1 in the heat sink holes 56.1, 56.2, 56.3. The heatsink holes 56.1, 56.2, 56.3 may be pre-threaded or threaded by means ofself-tapping bolts or screws 1.

FIG. 9 shows the electronic control unit 100 in the assembled state. Thesecond power board 40 with the second electronic components 41 on thebottom side are attached the to the heat conduction surfaces 52 of thetop side of the heat sink 50. The second electric motor connector 90comprises three second electric phase pins 92.1, 92.2, 92.3 arranged ina second electric motor connector housing 91. The second electric motorconnector housing 91 comprises further connection pins for connectionwith sixth connection pin holes in the second power board 40.

Further, the three second electric phase pins 92.1, 92.2, 92.3 compriseat ends opposite of the ends for connecting with corresponding electricmotor pins (not shown) of the electric motor several second power boardconnection pins for electrically connecting these with the second powerboard 40. Further, the second electric motor connector housing 91comprises second electric motor connector housing through holes forguiding bolts 1 therethrough for connection of the second power board 40to the heat sink holes 56.1, 56.3 of the heat sink 50 by means of thesecond electric motor connector housing 91.

Further bolts 1 are guided through corresponding through holes in thesecond power board 40 for connection to the heat sink holes 56.2, 56.4of the heat sink 50. Here, the second power board 40 is attached to thetop side of the heat sink 50 with its bottom side. The second powerboard 40 also comprises second power board recesses 42.1, 42.2, 42.3through with the first electric phase pins 82.1, 82.2, 82.3 of the firstelectric motor connector 80 are guided.

All bolts 1 are fastened such that the second power board 40 is fastenedto the heat sink 50 and the heat sink 50 is fastened to the connectorplate 10. The heat sink 50 is thereby sandwiched in between the firstpower board 30 and the second power board 40. The logic board 20 issandwiched in between the first power board 30 and the heat sink 50. Theelectric phase pins 82.1, 82.2, 82.3, 92.1, 92.2, 92.3 extend out of thesecond power board 40 and in particular beyond the heat sink projections57.1, 57.2, 57.3 such that they may be connected with the electric motorpins of the electric motor. The venting element may be inserted into theventing opening 13 after inserting the electronic control unit 100 intothe housing 210.

FIG. 10 shows the process of inserting the electronic control unit 100into the housing 210 of the electric power steering system 200. The heatsink projections 57.1, 57.2, 57.3 act as guides during this process.

FIG. 11 shows a cross section through a part of the electric powersteering system 200 having the housing 210. Therein, the housing 210 isnot yet crimped into the groove 51 of the heat sink 50. However, theoperation of crimping is indicated by an arrow referenced with thedirection of force F of the crimping operation. Thereby, the housing 210is plastically deformed and extends into the groove 51 of the heat sink50. The heat sink 50 and the housing 210 thereby become attached to oneanother and thermally coupled.

Further, the circumferential outer surfaces 58.1, 58.2 of the heat sink50 are attached to the inner surface 211 of the housing 210 for thermalcoupling and allowing the heat sink 50 to dissipate heat generated bythe two power boards 30, 40 attached to the heat sink 50 through thehousing 210 into the environment. Also, the heat sink projections 58.1,58.2, 58.3 may be arranged to rest on the inner rim 212 inside of thehousing 210.

The housing 210 is further sealed by means of the circumferentialsealing 12 of the connector plate 10 of the electronic control unit 100against its inner surface 211. The connector plate 10 is therebydesigned as a cap of the housing 210. Further, as can be seen in thiscross section, the first electric phase pins 82.1, 82.2, 82.3 are to beelectrically connected to electric motor pins of the electric motor ofthe electric power steering system 200.

LIST OF REFERENCE SIGNS

10 Connector plate

11 Plug connector

12 Sealing

13 Venting opening

15 Signal connectors

16 Second power connector

17 First power connector

18 Dome

20 Logic board

21 First electronic component

30 First power board

31 Second electronic component

32 First power board recess

33 Power board through hole

40 Second power board

41 Third electronic component

42 Second power board recess

50 Heat sink

51 Groove

52 Heat conduction surface

53 Heat sink cutout

54 Heat sink through hole

55 Heat sink recess

56 Heat sink hole

57 Heat sink projection

58 Circumferential outer surface

59 Heat sink edge

60 Second logic connector

61 Second logic connector housing

70 First logic connector

71 First logic connector housing

80 First electric motor connector

81 First electric motor connector housing

82 First electric phase pin

90 Second electric motor connector

91 Second electric motor connector housing

92 Second electric phase pin

100 Electronic control unit

200 Electric power steering system

210 Housing

211 Inner surface

212 Inner rim

F force

1. An electronic control unit for an electric power steering system, theelectric power steering system including a housing and an electricmotor, the electronic control unit being arranged inside the housing andelectrically connected to the electric motor, the electronic controlunit comprising: a first power board having a first electric motorconnector for electric connection with the electric motor, a secondpower board having a second electric motor connector for electricconnection with the electric motor, a connector plate having at leastone plug connector, the at least one plug connector electricallyconnecting the connector plate with the first power board via at leastone first power connector, and with the second power board via at leastone second power connector, wherein the at least one first powerconnector is shorter than the at least one second power connector. 2.The electronic control unit according to claim 1, wherein the connectorplate is connected to the first power board via two first powerconnectors and to the second power board via two second powerconnectors, wherein both first power connectors are shorter than bothsecond power connectors.
 3. The electronic control unit according toclaim 1, wherein the at least one first power connector and/or the atleast one second power connector are provided as metal strips.
 4. Theelectronic control unit according to claim 1, wherein the at least onesecond power connector has at least 120% of the length of the firstpower connector.
 5. The electronic control unit according to claim 1,wherein each of the first power board and the second power board isprovided with three phases of electricity to supply three-phase electricpower to the electric motor.
 6. The electronic control unit according toclaim 1, wherein a logic board is sandwiched in between the first powerboard and the connector plate.
 7. The electronic control unit accordingto claim 1, wherein the first power board comprises at least one firstpower board recess through which the at least one second power connectorextends to the second power board.
 8. The electronic control unitaccording to claim 1, further comprising a heat sink sandwiched inbetween the first power board and the second power board.
 9. Theelectronic control unit according to claim 8, wherein the heat sinkincludes heat sink through holes, and the first power board is securedto the heat sink by bolts passing through the heat sink through holesand being fastened in domes extending from the connector plate.
 10. Theelectronic control unit according to claim 8, wherein the heat sinkincludes heat sink holes and the second power board is secured to theheat sink by bolts fastened in the heat sink holes.
 11. The electroniccontrol unit according to claim 8, wherein the heat sink includes atleast one heat sink recess for the at least one second power connector,the at least one second power connector extending from the connectorplate through the at least one heat sink recess inside of the heat sinkto the second power board.
 12. The electronic control unit according toclaim 8, wherein the heat sink includes a heat sink cutout, and a secondlogic connector extends from the logic board through the heat sinkcutout to the second power board.
 13. The electronic control unitaccording to claim 12, wherein the first electric motor connector fromthe first power board extends through the heat sink cutout forconnection with the electric motor of the electric power steeringsystem.
 14. The electronic control unit according to claim 8, whereinthe heat sink includes heat sink projections projecting from the heatsink beyond the first power board and the second power board, and beingarranged to rest on an inner rim inside of the housing of the electricpower steering system.
 15. An electric power steering system comprising:an electronic control unit according to claim 1; an electric motorelectrically connected to the first power board by the first electricmotor connector and to the second power board by the second electricmotor connector.